1. Field of the Invention
The present invention relates to an image forming apparatus that has a function of outputting data to an external device.
2. Description of the Related Art
Conventionally, due to fluctuation in spectral sensitivities of a charge coupled device (CCD) or an infrared-ray cut filter, and deterioration with time and use of an optical system, a read value of a scanner in reading image data varies depending on a unit. Even when the identical color document is read, each of the units outputs a different image signal. As a result, an image output to be displayed or printed by each of the units appears in different colors.
In a conventional technology for adjusting the difference in color, an image forming apparatus performs a hue-division-masking color-correction processing. The image forming apparatus includes a unit that calculates a masking coefficient based on a value of an input image signal obtained by reading an original document of which a spectral characteristic corresponding to a point where hue is divided is known, and C, M, Y, and K recording values of a developing unit optimal for the reproduction of the color of the original document. Moreover, an image forming apparatus may include a unit that calculates a masking coefficient by a difference value between an output image signal obtained by converting the input image signal obtained by reading an original document, a spectral characteristic of which is known by a predetermined masking coefficient, and an output value obtained by converting, with the predetermined masking coefficient, an input image signal obtained when the original is read by a reading apparatus having a standard spectral characteristic. Such technologies are disclosed in, for example, Japanese Patent Application Laid-Open No. 2002-290761.
In an image processing method according to another conventional technology, a reference chart having color images of different gradation levels is read by a reading unit to create the correction data of the reading unit based on the image data of the read reference chart and reference data stored in advance in association with the color images of the different gradation levels. The image output by the output unit based on the reference data for the correction of the output unit is read by the reading unit corrected by the created correction data. Based on the read image data, correction data of the output unit is created. Such a technology is disclosed in, for example, Japanese Patent No. 2643951.
In still another conventional technology, an image processing apparatus corrects a color represented by a color image signal to be a color suitable for an output apparatus from which the color image signal should be output. This image processing apparatus includes a hue-area judging unit that determines a hue area that includes, among plural hue areas formed to include a plane in a color space parallel to a brightness axis as a boundary, a signal color represented by the color image signal and a correction unit that corrects a signal color according to the hue area. Such a technology is disclosed in, for example, Japanese Patent Application Laid-Open No. 2004-13361.
With the recent development of communication technologies, a situation surrounding color copying apparatuses has significantly changed. A large-scale image formation system in which more than one color copying apparatus is connected via the Internet or the like to provide the transmission and reception of data among plural color copying apparatuses has been widely used.
In the large-scale image formation system, image data read by a scanner in a color copying apparatus is sent to another color copying apparatus and an image processing unit (IPU) or a printing unit in the color copying apparatus that has received the image data can perform image processing for printing.
For example, when an original document is desired to be copied in a large quantity in a short period of time, the original document is read by a scanner in one color copying apparatus, and the read image data is sent to plural other color copying apparatuses. Thus, the read image data can be printed out by plural units of color copying apparatuses simultaneously.
In another example, when original documents existing at more than one location are desired to be collectively copied at one location, the original documents are read by a scanner in a color copying apparatus in each location and the read image data are sent to one color copying apparatus. Thus, the original documents in different places can be printed by one color copying apparatus.
However, in the conventional technologies, when plural color copying apparatuses are connected to provide data transmission and reception and a color copying apparatus different from a color copying apparatus that has read the original document performs printing, a color reproducibility is low compared to when a single color copying apparatus performs printing because a read value of a scanner in reading image data varies depending on a unit even when the identical color document is read.
An image processing parameter used for image processing by a color copying apparatus is obtained by calibrating a scanner and a printing unit in the color copying apparatus in pairs. Thus, all color copying apparatuses do not always store therein the same image processing parameter. However, in the conventional technology, a color copying apparatus different from a color copying apparatus that has read the original document performs image processing to print an image. Thus, a combination of the scanner that has read the original document and the printing unit that has performed the printing is different from a combination that was calibrated. Consequently, when image processing parameter of the color copying apparatus that has read the original document and the image processing parameter of the color copying apparatus that has received the image data are different, the color reproducibility is low compared to when a single color copying apparatus performs printing.
The problems described above are more conspicuous, when one original document is read by one color copying apparatus, and read image data of the original document is printed by plural color copying apparatuses. Copies having unequal color reproducibility are printed in a large quantity.
Similarly, the problems are conspicuous when original documents located at more than one location are collectively printed at one location by one color copying apparatus.